[bikerhifinut]

To add to David and GJ's excellent advice, I did once try a 5751 in the V1 position and unsurprisingly it had no effect whatsoever on the overall sensitivity of the amp. in any case the gain difference isn't that much different to an ECC83/12AX7. There are those who claim it gives a "darker" sound whatever that means. To me it means the frequency response has been skewed to cause an earlier than normal HF roll off...................... Add to that the exponential increase in the price of NOS 5751 in recent years and thats a lot of mugs of coffee whilst enjoying the music.

I've been using the stereo20 into a pair of Quad ESL989 for a week or two now and in its bog standard form so to speak, it's doing the job handsomely and when you consider these speakers need about 3W up their terminals just to make a normal (i.e. non deafening) room filling sound, then on transients the amps probably giving its full 12W before clip at times and it doesn''t sound stressed. As I type this I have plugged in an old mitsubishi power amp with LED bargraph power meters which on the final section of mike oldfields Ommadawn LP is telling me that its hitting between 8 and 13W on transients. Its lying of course but all the same.............

If you are thinking to use the Leak as your main amp its worth experimenting with a "pot in a box". Granted if you like tone controls and a balance control then you seem more than capable of knocking up a circuit based around a couple of op amps with a baxandall feedback tone control.
Or have a shuftie on the internet auction sites like ebay and you'll find a plethora of modules either ready built or in kit form that actually work rather well.

A.